Recent decades have been characterized by major trends toward widespread ecological awareness and health-consciousness. New needs have arisen for self powered recreational vehicles which don't consume fuel energy or pollute the atmosphere; along with a resurgence of popularity of the conventional bicycle, there has developed an increasing demand for alternative human-powered vehicles in forms which depart radically from the bicycle. Also, as part of the health-consciousness trend, the search for new exercise products has produced devices which provide new ways to exercise different muscles and parts of the body, for example treadmills and simulated stair-climbing machines. Some of these exercise machines consume electric power, and thus fail to be entirely ecological. Many of these machines are for indoor use, even though the benefits of exercise would be greatly enhanced if, for example, special leg movement exercises could be combined with outdoor mobility with its advantages of fresh air and ever-changing scenery.